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[css-font-loading] maintaining invariants of a FontFaceSet’s set entries

From: Cameron McCormack <cam@mcc.id.au>
Date: Sun, 22 Mar 2015 12:59:05 +1100
To: www-style@w3.org
Message-ID: <20150322015904.GA19946@wok.mcc.id.au>
Before the spec was change to make FontFaceSet setlike, there were a few
requirements on how the FontFace objects in a FontFaceSet were to be
maintained.  We need to add some of these back.

1. It used to be required that CSS-connected FontFace objects all
appeared before the other FontFace objects in a FontFaceSet.  Now there
is no such requirement.  It is required that they are kept in document
order, but doesn’t say anything about how they are placed relative to
the other FontFaces.

2. Calling FontFaceSet.add() with a CSS-connected FontFace object used
to throw an InvalidModificationError.  I don’t think there’s a good
reason to allow CSS-connected FontFaces in multiple FontFaceSets.  So
how about we throw in that situation, and ignore it if you try to add a
CSS-connected FontFace to the FontFaceSet it is already in (which is the
behaviour of a standard Set’s add method).

3. Similarly, FontFaceSet.delete() used to throw when trying to remove a
CSS-connected FontFace.  Whether an exception is thrown or the request
is ignored, I don’t particularly mind.  Ignoring the request is probably
implied by the requirement to keep all CSS-connected FontFaces in there
by §4.2, but should be made explicit somewhere.  That would be
consistent with having clear() not throw because it is attempting to
remove the CSS-connected entries, too.

Cameron McCormack ≝ http://mcc.id.au/
Received on Sunday, 22 March 2015 01:59:32 UTC

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